The present invention relates to polyester compositions, containing polymeric liquid crystals (LCP) suitable for the preparation of stretched articles, such as films and fibres, endowed with high mechanical properties, particularly a high elastic modulus.
It is known that liquid crystals (LCP) are used as a reinforcing material of thermoplastic polymers to improve their mechanical properties. The improvement is shown when the LCP quantity is at least 10% by weight of the polymeric matrix. Quantities lower than 5% determine under the conditions of experimental use only marginal increases.
The lowest concentrations used in literature do not have values lower than 1-2% by weight. This is due to the fact that with these low concentrations, and under the experimental use conditions there is no improvement of the resin mechanical properties.
The improvements, moreover, depend on the degree of stretching carried out. Stretching ratios of at least 20:1 are necessary in the case of cooled filaments at the extruder exit to obtain the highest increases. In the case of films where the practicable stretching ratios are generally between 2:1 and 10:1, there are no significant improvements of consequence of the insufficient molecular orientation obtainable (A. M. Sukhadia et al.--Intern. Polymer Processing VII (1992) 3, 218-228).